The invention relates to a method for the evaluation of information stored in bar codes composed of characters in accordance with the preamble of claim 1.
The method relates, on the one hand, to the use of manually guided light receiving devices, which are also referred to as bar code readers, can be designed as so-called pen readers and are manually guided over the bar code to be read. The pen reader emits light, in particular laser light, which is reflected from the bar code. The reflected light is detected by the pen reader and processed in an evaluation unit.
The method relates, on the other hand, to a stationary bar code reader (slot reader) past which the bar codes or the objects provided with the bar code are manually moved. In the case of a bar code reader of this type, the bar codes are irradiated from a stationary light source, in particular a laser light source. The light reflected from the bar code is detected by a stationary receiving device and processed by a processing unit.
In principle, the method relates to all evaluation methods in which a non-uniform relative movement is carried out between a light receiving device and a bar code from which light emitted by a light source is reflected.
The following definitions are used for the description:
A bar code is realized or applied to an object in accordance with a specific symbol standard (2/5, CODE39, EAN, CODE128, etc.).
A symbol, or bar code, is composed of a series of characters.
Each character consists of a predetermined number of dark bars with interspaces lying between them. The bars and spacings are also referred to as "elements". Within the characters, the successive bars and spacings can have different widths. This combination is unique to the symbols. These characters can be used, for example, to represent numbers, letters or else check characters.
The grid dimension and the nominal width of the smallest element of which a character can be composed are measured transversely with respect to the extent of the bars and spacings.
The nominal width of a character is a defined constant for each symbol and is expressed as a multiple of the grid dimension.
The method by which the data which depend on the width of each individual element are obtained is referred to as the scanning operation. The scanning operation can be carried out manually or by means of an automatic mechanism. It converts the width of each element into the time which is required for scanning a character. This time corresponds to the width measured by the bar code reader.
It is essential that, at the end of the acquisition of information contained in a bar code, the size of each individual element of which the code is composed is acquired. The analysis and processing of the data, which results in a conversion of the dimensions of the different elements into a sequence of ASCII characters, are referred to as decoding.
The quality of the decoding method is defined by the probability of obtaining a correct result.
It has emerged that the relative movement between the light receiving device and the bar code to be acquired is particularly non-uniform when the scanning operation is carried out manually. There is normally an acceleration at the start of the scanning operation and a deceleration at the end. This leads to distortion of the information which is read.
In a known method of this type for the evaluation of information, it is assumed that the scanning velocity during the scanning of an individual character is constant. In any case the scanning reliability based on this hypothesis is not adequate. This is due to levels of distortion caused by the non-uniform velocity during the scanning process.